Optics and Precision Engineering, Volume. 19, Issue 2, 200(2011)
Direct observation of molecular structural change during intersystem crossing by real-time spectroscopy with a few optical cycle lasers
The ultrafast spectroscopy by a sub 5 fs pulse laser was applied to the simultaneous study of electronic relaxation and vibrational dynamics in RuⅡ(TPP)(CO). The signals due to 1Qx(1,0)(π,π*) and 1Qx(0,0)(π,π*) are thought to decay in a sequential order from the higher energy states to the lower energy states in the sequences 1Qx(1,0)(π,π*)→1Qx(0,0)(π,π*)→3(d,π*)→3(π,π*) and 1Qx(0,0)(π,π*)→3(d,π*)→3(π,π*). The electronic lifetimes of 1Qx(1,0)(π,π*),1Qx(0,0)(π,π*),3(d,π*), and 3(π,π*) are determined to be (230±70) fs, (1150±260) fs, (2150±360) fs and larger than 4.8 ps, respectively. The lifetimes of 3(d,π*), and 3(π,π*) are estimated to be (2 150 ± 360) fs and larger than 4.8 ps, respectively. The lifetime of 1Qx(1,0)(π,π*) determined to be (230 ± 70) fs, is in relatively good agreement with the step-down time of (190±40) fs for the transition time from 1Qx(1,0)(π,π*) to 1Qx(0,0)(π,π*) calculated from the energy decay rate in the dynamic Stokes-shift process. The spectrogram analysis shows that the time dependent changes in the vibrational spectrum is associated with the spin state change from the Franck-Condon state in the excited singlet state to the triplet state via the curve crossing point or conical intersection between the singlet and triplet potential surfaces. It is found that the dynamics is can not be expressed in terms of the simple single exponential decay of the spectrogram signal of singlet and exponential growth of the triplet vibration spectrogram signal. In stead, the vibrational spectral change takes place with more complex dynamics. At first, the decay of the singlet vibration spectrum takes place and then new vibrational spectrum which is different from singlet and triplet states appears. After the growth and decay of the new vibrational spectrum, the triplet state vibration spectrum starts to grow. The dynamics at first looks different from that of electronic spectra. The reason of the apparent difference can be explained in the following way. The vibrational spectral change could sensitively detect the structural difference among the singlet sate and triplet state in their equilibriums and that of transition state or state close to the conical intersection.
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TAKAYOSHI KOBAYASHI. Direct observation of molecular structural change during intersystem crossing by real-time spectroscopy with a few optical cycle lasers[J]. Optics and Precision Engineering, 2011, 19(2): 200
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Received: Oct. 8, 2010
Accepted: --
Published Online: Mar. 30, 2011
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CSTR:32186.14.